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9 May 2018 Micro-structured fiber Bragg grating based pressure sensors in a downhole-like hydrogen rich environment
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The applicability of fiber Bragg gratings written in highly birefringent Butterfly micro-structured optical fibers (MSFBG) for simultaneous High Pressure/High Temperature monitoring without a significant pressure/temperature cross sensitivity have recently been shown. This makes these MS-FBG sensors extremely interesting for downhole monitoring in the Oil and Gas industry. However, an important effect to be taken into account for these applications is the presence of hydrogen, as hydrogen is known to diffuse into the fiber structure and therefore might affect the wavelength responses of the sensor element. In this paper, the effect of hydrogen gas on the MS-FBG sensor readings by monitoring the wavelength changes of the MS-FBG sensor in a hydrogen rich environment have been investigated.

In this experiments, two MS-FBG sensors were placed in a hydrogen test chamber: one with its fiber end sealed for pressure sensing and the other with its fiber end kept open for referencing purposes. It could be demonstrated that both sensors show a similar wavelength shift after some time and that due to the hydrogen diffusion, the pressure in the airholes of the sealed MS-FBG sensor equalizes the hydrogen pressure in the chamber. Furthermore, it could be demonstrated that the refractive index seen by the waveguide of the fiber is also affected. Based on all these observations, the influence of the hydrogen on the temperature and pressure measurement performance of the MS-FBG sensor is estimated, and a mitigation scheme that partially compensates for this influence is discussed.
Conference Presentation
© (2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Ji-Ying Huang, Jan Van Roosbroeck, Johan Vlekken, Damien Kinet, Antonio Bueno Martinez, Thomas Geernaert, Francis Berghmans, Bram Van Hoe, Eric Lindner, and Christophe Caucheteur "Micro-structured fiber Bragg grating based pressure sensors in a downhole-like hydrogen rich environment", Proc. SPIE 10680, Optical Sensing and Detection V, 106800L (9 May 2018);

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